Thanks Niggle, that helps. With the stepper motors I'm wondering what the vital stats are for GUS.-Are high torque motors needed for the arms and the extruder?- What would be the minimum torque that I could get away with?

I'm having trouble finding the same specs as the ones at QU-BD. I've got a few stepper motors that I can play with, but I don't have all the specs on them, though one looks to be a beefy NEMA 17 that could work.

E-bay is where I got my hobbed pulley, so I'm not adverse to shopping there, I just worry about picking the right motors.

There are places online to get the Bowden tube, I'm just looking for a reasonable price.

The hot end will be the hardest one as QU-BD makes the clones. I could get a real ubis hot end or jump into the j-head pool. I'm not sure about the j-head as this is a vital part to be thinking about deviating from considering my lack of experience with them.

J-heads are tried and tested, just like Ubis hot ends. I've had excellent results with both.

The nozzle size is harder to change on the J-head vs Ubis, but I think the J-head design potentially can have a sharper heat break (a good thing) due to the greater potential for active cooling. My Printrbot Ubis has jammed twice when I left the hotend on without active cooling, but if you only enable the heater when the print is ready, you shouldn't have any problems there.

FWIW, SpiderPig's prints were all with a J-head with 0.35 nozzle, using Johann's fan shroud.

Also, regarding stepper torque, I would go with as high torque as you can find. There's enough friction in the system that a little extra torque would come in handy. My Kysans were near the edge of the passive cooling limit (~1A stepper driving setting) and at the most-extended position would sometimes slip. Ultimachine's web site has the torque specs for these.

This is Chris, you contacted me through 3DHubs. I usually lurk around here but it's been a while since I browsed the forum. Let me know if you need any parts, I got a bunch. BTW, don't get the anUBIS, it's not that good. I have two and only got one of them working. Too much back pressure when extruding, even on a direct drive setup. Using it for a bowden setup may chew up the filament.

If you need some assistance in acquiring printed parts, feel free to contact me. I could print a few parts for free but really, I would like to see a working Simpson here in Boston. Nick would be happy!

@brandonh @gyronictonicThose are some good arguments for the j-head, and I'm leaning that way. It is very battle tested and the parts are widely avaialable.

@gyronictonicThank you for your offer of help. I will definitely call upon you if I get irrevocably stuck and am in need of a few random bits of magic 3D printer parts. With everyone's help here, I think I'll be able to source everything that I need shortly. I will let you know if I get stuck and need some parts printed as well.

As I understand it, and I could easily be mistaken, there are two reasons for using fans.

The first is that heat from the heater block creeps up the extruder enough to soften the filament before it gets to the heater block. This leads to the filament expanding in the top of the hotend, eventually jamming there. Hotend designers try to mitigate this with a thermal break just above the heater block. Passive cooling (fins) and active cooling (air flow over the upper shaft and any fins) help.

Another issue is that small fans are gloriously inefficient. Air doesn't like being pushed through small passages so the amount of cooling from a small fan is limited. A shrouded fan (squirrel cage style) is recommended for cooling the hotend because it is far more efficient than a plain fan of the same size. The Makerbots use a shrouded fan with some success.

The second is to cool the extruded plastic so that it doesn't flow once it fuses with the print. This is an interesting problem since you need to give the extruded filament time to fuse but not time to flow afterwards, doing this without pushing enough air at the print to distort it. Further, you need this to work regardless of the direction the extruder is moving. However, the designs I have seen simply point a fan in the general direction of the tip of the extruder.

Another issue is that small fans are gloriously inefficient. Air doesn't like being pushed through small passages so the amount of cooling from a small fan is limited. A shrouded fan (squirrel cage style) is recommended for cooling the hotend because it is far more efficient than a plain fan of the same size.

For the GUS, I would not worry too much about the weight of the hub unless you have weak motors that run warm. Otherwise, you should be able to crank up the power slightly for the arm(s) carrying the extra weight. That is, if you have not already bought your motors, find ones that have more torque than those listed in the BOM.

@NiggleOK, that was my understanding of the situation as well with some important missing details added. The motors are purchased, and they are spec'd out just slightly higher than the ones in the BOM.

My mind keeps going to a system where a larger remote fan could be blowing air through one or more flexible tubes along with the bowden tube. Each would go to a specific section that needed it. I'm pretty sure this won't work as pressure would be needed and that's beyond the scope of my skills/budget/space. If my printer with anubis hot end comes soon then I can take a look at that myself to see if it will work. I'm trying to keep the added complications to a minimum, but I guess that I'll figure it out with either hot end.

Quick update on my build. My 3D printing mentor has been printing out the parts, and they are coming out pretty well. So far I have one arm and the hub put together. While I'm waiting for more parts, I'll start to wire things up. At this point I'm pleased with my progress, and hope that it goes smoothly.

I know that the GUS 2 is cooking, but since I already have the parts, I'm moving forward with this build.